The solid oxide fuel cell has a stack structure formed by stacking sheet bodies each of which comprises three layers of the electrolyte layer, a fuel electrode layer, an air electrode layer, and separators in alternating layers. In an air channel defined between the air electrode and the separator facing the air electrode layer, a SUS mesh made of stainless steel for electrically connecting both of them is confined. On the surface of the SUS mesh, previously by itself before the assembly of the stack structure, an Ag-plating treatment is performed and further a vacuum heat-treatment (heat-treatment under a negative pressure) is performed.
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1. A solid oxide fuel cell reactor which comprises:
a reaction member comprising an electrolyte portion containing a solid oxide electrolyte, a fuel electrode portion arranged integrally with said electrolyte portion and contacting a fuel gas to react said fuel gas, and an air electrode portion arranged integrally with said electrolyte portion and contacting an oxygen-containing gas to react said oxygen-containing gas;
other than said reaction member, an electrically conductive member made of metal containing iron and chromium, electrically connected with said air electrode portion to give and receive electrical power to and from said air electrode portion, wherein said air electrode portion and said electrically conductive member are physically fixed and electrically connected through a structure consisting of an electrically conductive adhesive metal fired film, an oxygen barrier metal layer and a layer containing cr2O3formed at the boundary between said electrically conductive member and said oxygen barrier metal layer; and
the thickness of said layer containing cr2O3 is 0.8 μm or less.
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3. The reactor according to
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1. Technical Field
The present invention relates to a reactor utilizing a reaction member comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas, and an air electrode portion arranged integrally with the electrolyte portion and contacting an oxygen-containing gas to react the oxygen-containing gas.
2. Background Art
Conventionally, as a reactor utilizing the above-described reaction member, a solid oxide-type fuel cell (Solid Oxide Fuel Cell: SOFC), a fuel gas reforming apparatus, and the like are known. For example, the SOFC described in a Japanese Patent Application Laid-Open (kokai) No. 2004-342584 will be explained below.
In the SOFC described in the above Japanese Patent Application, as the reaction member, a sheet body formed by stacking and firing a solid electrolyte layer as the electrolyte portion, a fuel electrode layer as the fuel electrode portion formed on the upper surface of the solid electrolyte layer, and an air electrode layer as the air electrode portion formed on the lower surface of the solid electrolyte layer is used. In this SOFC, a flat-plate stack structure, in which sheet bodies and metallic separators supporting the sheet bodies are stacked in alternating layers, is adopted.
For each sheet body, a fuel channel, through which a fuel gas (e.g., hydrogen gas) flows, is formed and defined in a space between the separator adjacent to the upper side of the sheet body (upper separator) and (the fuel electrode layer in) the sheet body, and an air channel, through which an oxygen-containing gas (e.g., air) flows, is formed and defined in a space between the separator adjacent to the lower side of the sheet body (lower separator) and (the air electrode layer in) the sheet body.
In the SOFC described in the above document, for each of the sheet bodies, an electrically conductive member (specifically, metal mesh or the like) for electrically connecting the upper separator and the fuel electrode layer of the sheet body is often confined in the fuel channel. It can be said that the electrically conductive member on the side of the fuel channel is a member which is electrically connected with the fuel electrode layer (fuel electrode portion) to give and receive electrical power to and from the fuel electrode layer (fuel electrode portion). As a material for the electrically conductive member on the side of the fuel channel, nickel or the like is generally used.
Similarly, for each of the sheet bodies, an electrically conductive member (specifically, metal mesh or the like) for electrically connecting the lower separator and the air electrode layer of the sheet body is often confined in the air channel. It can be said that the electrically conductive member on the side of the air channel is a member which is electrically connected with the air electrode layer (air electrode portion) to give and receive electrical power to and from the air electrode layer (air electrode portion). As a material for the electrically conductive member on the side of the air channel, metal containing iron, chromium as a main component, e.g., stainless steel (specifically, ferritic SUS or the like) is generally used.
Thus, when the electrically conductive members are respectively confined in the fuel channel and the air channel, the SOFC described in the above document is assembled and manufactures, for example, as follows. First, in a state in which an adhesive interposes at the bonded surfaces between the sheet body and the separator adjacent to each other, the sheet bodies and the separators are stacked in alternating layers with the electrically conductive members interposed on the side of the fuel channel and on the side of the air channel respectively. During the stacking process, in order to secure the reliability of the electrical connection between the upper separator and the electrically conductive member on the side of the fuel channel, as well as the reliability of the electrical connection between the lower separator and the electrically conductive member on the side of the air channel, by means of welding, diffusion bonding or the like, the electrical connection portion between the upper separator and the electrically conductive member on the side of the fuel channel may be previously fixed in an electrically connected state, as well as the electrical connection portion between the lower separator and the electrically conductive member on the side of the air channel may be previously fixed in an electrically connected state.
In addition, during the stacking process, in order to secure the reliability of the electrical connection between the fuel electrode layer of the sheet body and the electrically conductive member on the side of the fuel channel, electrically conductive adhesive paste (e.g., nickel paste, or nickel oxide paste) may be previously coated on the surface of the fuel electrode layer of the sheet body. Similarly, in order to secure the reliability of the electrical connection between the air electrode layer of the sheet body and the electrically conductive member on the side of the air channel, electrically conductive adhesive paste (e.g., silver paste, electrically conductive ceramic paste, or platinum paste) may be previously coated on the surface of the air electrode layer of the sheet body.
After the assembly of the stack structure as described above, in order to solidify the above-described adhesive, and in order to solidify (fire) the above-described adhesive paste when the adhesive paste is coated, a heat-treatment is performed on the stack structure. Thereby, an SOFC having a stack structure is completed.
The above-described electrically conductive member (metal mesh or the like) made of stainless steel on the side of the air channel will be discussed below. The electrically conductive member made of stainless steel is likely to have chromia (Cr2O3) formed on the surface thereof at a high temperature of about 400° C. or higher and in the air. Accordingly, when a heat-treatment at 400° C. or higher is performed during the manufacturing (assembling) process of the stack structure as described above, it is likely that chromia is formed in the surface of the electrically conductive member. In addition, since the working temperature of SOFC is generally 400° C. or higher, chromia may be formed on the surface of the electrically conductive member during the operation of SOFC as well.
The chromia may be formed at the boundary between the electrically conductive member and the air electrode layer of the sheet body (i.e., on the surface of the electrical connection portion), when the electrically conductive member and the air electrode layer of the sheet body directly contact each other. Further, as described above, the chromia may be formed at the boundary between the electrically conductive member and the adhesive paste (i.e., on the surface of the electrical connection portion), when the adhesive paste interposes between the electrically conductive member and the air electrode layer of the sheet body. This is because air (oxygen) can be supplied to the boundary between the electrically conductive member and the adhesive paste through a large number of pores existing in the adhesive paste.
Chromia has a large electrical resistance. Therefore, when chromia is formed at the boundary between the electrically conductive member and the air electrode layer of the sheet body (or at the boundary between the electrically conductive member and the adhesive paste) (i.e., on the surface of the electrical connection portion) as described above, problems such as the increase in the electrical resistance (internal resistance) of the SOFC as a whole and the decrease in the output of the SOFC as a whole may occur.
Accordingly, an object of the present invention is to suppress the formation of chromia on the surface of an electrical connection portion between an air electrode portion and an electrically conductive member made of stainless steel for giving and receiving electrical power to and from the air electrode layer during the manufacturing process of a reactor utilizing a reaction member comprising an electrolyte portion, a fuel electrode portion, and an air electrode portion.
The reactor according to the present invention comprises a reaction member (comprising an electrolyte portion containing solid electrolyte, a fuel electrode portion arranged integrally with the electrolyte portion and contacting a fuel gas to react the fuel gas, and an air electrode portion arranged integrally with the electrolyte portion and contacting an oxygen-containing gas to react the oxygen-containing gas) and, other than the reaction member, an electrically conductive member made of metal containing iron and chromium which is electrically connected with the air electrode portion to give and receive electrical power to and from the air electrode portion. The electrically conductive member is preferably made of stainless steel.
In the case where the reactor functions as an SOFC, oxygen ions can be conducted within the electrolyte portion. The air electrode portion facilitates a reaction creating oxygen ions from an oxygen-containing gas (e.g., air) on its surface and oxygen ions can be conducted within the air electrode portion. The fuel electrode portion facilitates a reaction creating electrons by reacting oxygen ions with a fuel gas.
In an aspect of the reactor according to the present invention, a metal film is formed on the surface of at least the portion on the electrically conductive member, which is electrically connected with the air electrode portion, and a first heat-treatment is performed on the electrically conductive member after the formation of the metal film, in a state in which an ambient pressure is adjusted to a negative pressure lower than an atmospheric pressure, and the electrically conductive member and the air electrode portion are electrically connected by electrically connecting the air electrode portion and a post-heat-treatment metal film surface, which is the surface of the portion on which the metal film is formed and then the first heat-treatment is performed.
The producing method of the reactor includes:
a metal film forming step wherein metal film is formed on the surface of at least the portion on the electrically conductive member, which is electrically connected with the air electrode portion,
a first heat-treatment step wherein the first heat-treatment is performed on the electrically conductive member after the metal film forming step, in a state in which an ambient pressure is adjusted to a negative pressure lower than an atmospheric pressure; and
an electrically connecting step wherein the electrically conductive member and the air electrode portion are electrically connected by electrically connecting the air electrode portion and a post-heat-treatment metal film surface, which is the surface of the portion with the metal film formed thereon, after the first heat-treatment step.
Herein, the metal film is preferably formed by metalizing plating. In this case, during the metal film forming step, the metal film is formed by metalizing plating.
In order to suppress the oxidization of the surface, i.e., the formation of chromia on the surface, while maintaining the electrical conductivity of the electrically conductive member made of iron-series metal containing chromium (e.g., stainless steel), it is supposed to form an electrically conductive oxygen barrier layer (metal film) for suppressing the oxygen supply to the surface of the electrically conductive member. As the oxygen barrier layer (metal film), a dense (with low porosity) metal-plated layer is preferably formed. However, the inventors found out that, even if metal film such as a metal-plated layer has been formed, during the subsequent manufacturing process of the reactor, or during the operation of the reactor, when the electrically conductive member (after the formation of metal film) is placed at a high temperature, chromia may be still formed on the surface of the electrically conductive member (i.e., at the boundary between the electrically conductive member and the metal film) (will be described later in detail). It is believed that this is because part of the metal film is detached from the surface of the electrically conductive member due to not only the lack of adhesion strength of the metal film, but also the difference of the coefficients of thermal expansion between the electrically conductive member and the metal film, and, through the detached region, oxygen can be supplied to the surface of the electrically conductive member.
Therefore, as a result of further investigation, the inventors found out that when the heat-treatment is performed on the electrically conductive member after the formation of metal film, in a state in which an ambient pressure is adjusted to a negative pressure lower than an atmospheric pressure (a negative pressure condition), it is difficult for chromia to be formed on the surface of the electrically conductive member (i.e., at the boundary between the electrically conductive member and the metal film), even though the electrically conductive member (after the formation of the metal film and the heat-treatment) is placed at a high temperature, during the subsequent manufacturing process of the reactor, or during the operation of the reactor (will be described in detail). It is believed that this is because, in a negative pressure condition where the concentration of oxygen is low in the atmosphere (i.e., a state wherein even if the metal film detached, it is difficult to provide the surface of the electrically conductive member with oxygen), the boundary between the electrically conductive member and the metal film is reacted and integrated by the heat-treatment, and thereby a strong oxygen barrier layer is formed on the surface of the electrically conductive member.
The above-described configuration is based on such knowledge. According thereto, by electrically connecting the surface of the portion on which the metal film is formed and then the first heat-treatment is performed (post-heat-treatment metal film surface) with the air electrode portion, the formation of chromia on the surface of the electrical connection portion with the air electrode portion on the electrically conductive member (at the boundary between the electrically conductive member and the metal film) can be suppressed, even though the electrically conductive member is placed at a high temperature, during the subsequent manufacturing process of the reactor, or during the operation of the reactor. As a result, the increase in the electrical resistance (internal resistance) of the reactor as a whole due to the oxidization of the surface of the electrical connection portion with the air electrode portion on the electrically conductive member can be suppressed. Accordingly, for example, when the reactor is an SFOC, the decrease in the output of the SOFC as a whole can be suppressed.
Further, in accordance with the above-described configuration, even when the working temperature is high, 500 to 1000° C., as in the case of SOFC, the presence of the above-described strong barrier lay makes it difficult for chromia to be formed on the surface of the electrically conductive member during the operation of the reactor. Accordingly, even though the reactor has been operated for a long period, the increase of in the electrical resistance of the reactor as a whole can be suppressed.
In order to suppress the increase in the electrical resistance at the electrical connection portion between the electrically conductive member and the air electrode portion, it is enough to form the metal film (and perform the heat-treatment) only on the surface of the electrical connection portion with the air electrode portion on the electrically conductive member. However, the metal film may be formed (and the heat-treatment may be performed) on the whole surface of the electrically conductive member. When a metalizing plating is performed in order to form the metal film, for example, a silver-plating, a zinc-plating may be used as metalizing plating. After taking into account the fact that noble metal unlikely to be oxidized, as the metalizing plating, it is preferred to use a silver-plating. Thereby, the increase of the electrical resistance of the reactor as a whole due to the oxidization of the surface of the metal-plated portion (especially, the surface of the electrical connection portion with the air electrode portion) can be suppressed.
In addition, chromium poisoning of the air electrode portion from the electrical conductivity of the electrically conductive member made of iron-series metal containing chromium (e.g., stainless steel) can be suppressed. The term “chromium poisoning of the air electrode portion” means that chromium is flown apart therefrom and attaches to the air electrode portion by subjecting the iron-series metal containing chromium (e.g., stainless steel) to a high temperature. The chromium poisoning may deactivate the air electrode portion and, as a result, lower the output of the reactor.
In the reactor according to the above-described present invention, it is preferred that, in a state in which the post-heat-treatment metal film surface and the air electrode portion are connected through an electrically conductive adhesive paste, a second heat-treatment is performed to solidify (fire) the adhesive paste and thereby the post-heat-treatment metal film surface and the air electrode portion are electrically connected. In this case, the electrically connecting step includes the second heat-treatment step wherein, in a state in which the post-heat-treatment metal film surface and the air electrode portion are connected through an adhesive paste, the second heat-treatment is performed to solidify (fire) the adhesive paste and thereby the post-heat-treatment metal film surface and the air electrode portion are electrically connected.
Herein, as the adhesive paste, silver paste, electrically conductive ceramic paste, platinum paste or the like may be used. Among them, silver paste is preferably used, since it is low in cost, unlikely to be oxidized, and low in electrical resistance. The adhesive paste may be previously coated on the surface of the electrical connection portion with the “post-heat-treatment metal film” on the air electrode portion, or may be previously coated on the surface of the electrical connection portion with the air electrode portion on the “post-heat-treatment metal film.”
As described above, by electrically connecting the “post-heat-treatment metal film” and the air electrode portion through the adhesive paste, the reliability of the electrical connection between the air electrode portion and the electrically conductive member can be secured.
In accordance with the investigation by the inventors, it was revealed that, in the heat-treatment (first heat-treatment) performed on the electrically conductive member after the formation of the above-described metal film (e.g., after a metalizing plating), the negative pressure (degree of vacuum) is preferably adjusted to be from 10−5 Pa to 10−1 Pa. Further, it was revealed that the temperature is preferably adjusted to be from 500° C. to 900° C. Furthermore, the duration time of the heat-treatment (first heat-treatment) is preferably from 10 minutes to 3 hours. They will be described hereinafter.
In the above-described reactor according to the present invention, the air electrode portion and the electrically conductive member are electrically connected through the metal film. For example, the electrically conductive member is made of stainless steel, and the metal film is made of Ag. Observation of the boundary between the electrically conductive member and the metal film revealed that although a “layer containing chromia (Cr2O3)” is formed at the boundary, the thickness of the “layer containing chromia (Cr2O3)” is extremely thin, 0.8 μm or less, immediately after the completion of the assembly of the reactor, or under a condition where the total operation period of the reactor is 100 hours or less. Such an extremely thin thickness of the “layer containing chromia (Cr2O3)” can suppress the increase of the electrical resistance (internal resistance) of the electrical connection portion between the electrically conductive member and the air electrode portion.
In the case where the reactor is an SOFC having a flat-plate stack structure, the reaction member is a sheet body formed by stacking and firing a solid electrolyte layer as the electrolyte portion, a fuel electrode layer as the fuel electrode portion formed on the upper surface of the solid electrolyte layer, and an air electrode layer as the air electrode portion formed on the lower surface of the solid electrolyte layer is used. In this SOFC, the sheet bodies and metallic separators supporting the sheet bodies are stacked in alternating layers. For each of the sheet bodies, a fuel channel, through which the fuel gas flows, is formed and defined in a space between the separator adjacent to the upper side of the sheet body (upper separator) and the sheet body, and an air channel, through which the oxygen-containing gas flows, is formed and defined in a space between the separator adjacent to the lower side of the sheet body (lower separator) and the sheet body. Further, for each of the sheet bodies, the electrically conductive member is confined in the air channel such that the electrically conductive member is electrically connected with both the lower separator and the air electrode layer of the sheet body. For each of the electrically conductive members, the metal film is formed on the surface of at least the portion on the electrically conductive member, which is electrically connected with the air electrode layer, and the first heat-treatment is performed on the electrically conductive member after the formation of the metal film, and the electrically conductive member and the air electrode layer are electrically connected by electrically connecting the air electrode layer and the post-heat-treatment metal film surface.
Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiment when considered in connection with the accompanying drawings, in which:
A reactor (solid oxide fuel cell) according to an embodiment of the present invention will next be described with reference to the drawings.
Overall Structure of Fuel Cell:
As shown on an enlarged scale within a circle A of
In the present embodiment, the electrolyte layer 11a is a dense fired body of YSZ (yttria-stabilized zirconia). The fuel electrode layer 11b is a fired body of Ni—YSZ (the fired body is a state after the later-described reduction process. It is a fired body of NiO—YSZ before the reduction process), and a porous electrode layer. The air electrode layer 11c is a fired body of USCF (lanthanum strontium cobalt ferrite) and a porous electrode layer. The electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c have different room-temperature-to-1000° C. mean thermal expansion coefficients of about 10.8 ppm/K, 12.5 ppm/K, and 12 ppm/K, respectively. In addition, a reaction preventing layer, for example GDC (gadolinium doped ceria), may be interposed between the air electrode layer 11c and the electrolyte layer 11a.
The sheet body 11 has a pair of cell through-holes 11d. Each of the cell through-holes 11d extends through the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c. The paired cell through-holes 11d are formed in the vicinity of one side of the sheet body 11 and in the vicinity of corresponding opposite ends of the side.
The separator 12 is formed from a Ni-based heat-resistant alloy (e.g., ferritic SUS, INCONEL 600, HASTELLOY or the like). The separator 12 formed from, for example, SUS 430, which is a ferritic SUS, has a room-temperature-to-1000° C. mean thermal expansion coefficient of about 12.5 ppm/K. Thus, the thermal expansion coefficient of the separator 12 is higher than the mean thermal expansion coefficient of the sheet body 11. Therefore, when the temperature of the fuel cell 10 changes, the difference in the amount of expansion and contraction is produced between the sheet body 11 and the separator 12.
The plane portion 12a is a thin, flat body having a thickness along the z-axis. The planar shape of the plane portion 12a is a square having sides (length of one side=L(<A)) extending along the x-axis and the y-axis.
The upper frame portion 12b is a frame body provided around the plane portion 12a (in a region in the vicinity of the four sides of the plane portion 12a; i.e., an outer peripheral region of the plane portion 12a) in an upwardly projecting condition. The upper frame portion 12b consists of a perimetric frame portion 12b1 and a jutting portion 12b2.
The perimetric frame portion 12b1 is located on a side toward the perimeter of the separator 12. The vertical section of the perimetric frame portion 12b1 (e.g., a section of the perimetric frame portion 12b1 whose longitudinal direction coincides with the direction of the y-axis, taken along a plane parallel with the x-z plane) assumes a rectangular shape (or a square shape).
The jutting portion 12b2 juts toward the center of the separator 12 from the inner peripheral surface of the perimetric frame portion 12b1 at one of four corner portions of the plane portion 12a. The lower surface of the jutting portion 12b2 is integral with the plane portion 12a. The shape of the jutting portion 12b2 as viewed in plane is generally square. The upper surface (plane surface) of the jutting portion 12b2 is continuous with the upper surface (plane surface) of the perimetric portion 12b1. The jutting portion 12b2 has a through-hole TH formed therein. The through-hole TH also extends through a portion of the plane portion 12a that is located under the jutting portion 12b2.
The lower frame portion 12c is a frame body provided around the plane portion 12a (in a region in the vicinity of the four sides of the plane portion 12a; i.e., an outer peripheral region of the plane portion 12a) in a downwardly projecting condition. The lower frame portion 12c is symmetrical with the upper frame portion 12b with respect to a centerline CL that halves the thickness of the plane portion 12a. Accordingly, the lower frame portion 12c has a perimetric frame portion 12c1 and a jutting portion 12c2 that are identical in shape with the perimetric frame portion 12b1 and the jutting portion 12b2, respectively. However, the jutting portion 12c2 is formed at the plane portion 12a in such a manner as to be diagonally opposite the jutting portion 12b2 as viewed in plane.
For convenience of description, of the paired separators 12, the separator 12 adjacent to the lower side of the sheet body 11 is referred to as a lower separator 121, and the separator 12 adjacent to the upper side of the sheet body 11 is referred to as an upper separator 122. As shown in
The entire perimetric portion of the sheet body 11 is sandwiched between the upper frame portion 12b (perimetric portion) of the lower separator 121 and the lower frame portion 12c (perimetric portion) of the upper separator 122. At this time, the sheet body 11 is arranged such that the air electrode layer 11c faces the upper surface of the plane portion 12a of the lower separator 121 and such that the fuel electrode layer 11b faces the lower surface of the plane portion 12a of the upper separator 122.
The entire perimetric portion of the sheet body 11 and the entire perimetric portion of the upper frame portion 12b of the lower separator 121, as well as the entire perimetric portion of the sheet body 11 and the entire perimetric portion of the lower frame member 12c of the upper separator 122, are sealed (bonded) to one another in an electrically insulated manner, whereby they are fixed to each another so as to make the relative movement impossible. A crystallized glass (may have an amorphous region left) is used as the seal material 13.
Thus, as shown in
Similarly, the lower surface of the plane portion 12a of the upper separator 122, the inner wall surface of the lower frame portion 12c (the perimetric frame portion 12c1 and the jutting portion 12c2) of the upper separator 122, and the upper surface of the fuel electrode layer 11b of the sheet body 11 define a fuel channel 22 through which a fuel containing hydrogen flows. The fuel flows into the fuel channel 22 through the through-hole TH of the lower separator 121 and the cell through-hole 11d of the sheet body 11 as indicated by an arrow of a solid line in
As shown in
The upper end (upper salient) and the lower end (lower salient) of the SUS mesh 31 contact the lower surface of the air electrode layer 11c of the sheet body 11 and the upper surface of the plane portion 12a of the lower separator 121, respectively. More specifically, as will be described later, the upper end of the SUS mesh 31 is fixed and electrically connected to the air electrode layer 11c through an Ag fired film, and the lower end of the SUS mesh 31 is fixed and electrically connected to the lower separator 121 by means of welding (or diffusion bonding). As will be described in detail later, for the SUS mesh 31, before being confined in the air channel 21, Ag-plating treatment and vacuum heat-treatment had been previously performed.
Similarly, the Ni mesh 32 (e.g., having an emboss structure), which is a flat sheet-like metal mesh made of Ni, is confined in the fuel channel 22. The wire diameter of the Ni mesh 32 is, e.g., from 0.05 to 0.5 mm. The upper end and the lower end of the Ni mesh 32 contact the lower surface of the plane portion 12a of the upper separator 122 and the upper surface of the fuel electrode layer 11b of the sheet body 11, respectively. More specifically, as will be described later, the upper end of the Ni mesh 32 is fixed and electrically connected to the upper separator 122 by means of welding (or diffusion bonding), and the lower end of the Ni mesh 32 is fixed and electrically connected to the fuel electrode layer 11b through an Ni fired film.
Thus, by virtue of the confinement of the SUS mesh 31 within the air channel 21, the electrical connection between the lower separator 121 and (the air electrode layer 11c of) the sheet body 11 can be secured, and by virtue of the confinement of the Ni mesh 32 within the fuel channel 22, the electrical connection between the upper separator 122 and (the fuel electrode layer 11b of) the sheet body 11 can be secured. Further, since the metal meshes 31, 32 are confined, the flow channel of a gas is restricted. As a result, the area (circulation area), viewed from the plane, where the electricity-generating reaction can substantially be produced due to the circulation of the gas can be increased in the air channel 21 and the fuel channel 22, whereby the electricity-generating reaction can effectively be generated in the sheet body 11.
In the thus-configured fuel cell 10, as shown in
(1/2)·O2+2e−→O2− (at air electrode layer 11c) (1)
H2+O2−→H2O+2e− (at fuel electrode layer 11b) (2)
Since the fuel cell (SOFC) 10 utilizes oxygen conductivity of the solid electrolyte layer 11a for generating electricity, the working temperature of the fuel cell 10 is generally 600° C. or higher. Accordingly, the temperature of the fuel cell 10 is raised from room temperature to the working temperature (e.g., 800° C.) by means of an external heating mechanism (e.g., a heating mechanism that uses a resistance heater or a heating mechanism that utilizes heat generated through combustion of a fuel gas).
The length of one side A of the planar shape (=square) of the sheet body 11 (accordingly, the separator 12) is 1.1 cm or more and 11 cm or less in the present embodiment. The thickness t1 of the sheet body 11 is uniform all over. In the present embodiment, the thickness t1 is 20 μm or more and 500 μm or less. The thickness of the fuel electrode layer 11b is greater than the thickness of the solid electrolyte layer 11a and the thickness of the air electrode layer 11c. Specifically, the rigidity of the fuel electrode layer 11b is the greatest among three layers, so that the fuel electrode layer 11b can serve as a support layer of the sheet body 11. For example, the thickness of the electrolyte layer 11a is 1 μm or more and 50 μm or less, the thickness of the fuel electrode layer 11b is 5 μm or more and 500 μm or less, and the thickness of the air electrode layer 11c is 5 μm or more and 200 μm or less.
The length L of one side of the planar shape (=square) of the plane portion 12a of the separator 12 is 1 cm or more and 10 cm. or less in the present embodiment. The width ((A−L)/2) of the “frame portion” (perimetric portion) of the separator 12 is 0.05 cm or more and 0.5 cm or less. Accordingly, the area of the plane portion 12a of the separator 12 as viewed in plane is 1 cm2 or more and 100 cm2 or less. The thickness t2 of the “frame portion” (perimetric portion) of the separator 12 is 200 μm or more and 1000 μm or less. The thickness tz of the plane portion 12a of the separator 12 is 50 μm or more and 100 μm or less.
Manufacturing and Assembly of Fuel Cell
Next, one example of a method of manufacturing and assembling the fuel cell 10 will be described.
Manufacturing Individual Members
Firstly, the manufacture of the individual members used for the assembly of the fuel cell 10 will be described.
Manufacturing Sheet Body
Firstly explained is the case in which the sheet body 11 used for the assembly of the fuel cell 10 is a fuel-electrode-support-type (the fuel electrode layer serves as a support substrate). In this case, a sheet (that is to become the fuel electrode layer 11b) made of NiO and YSZ is firstly prepared. Then, a ceramic sheet (YSZ tape) prepared by a green sheet process is laminated on the lower surface of the sheet. The resultant laminate is fired at 1400° C. for one hour. Subsequently, a sheet (that is to become the air electrode layer 11c) is formed by a printing process on the lower surface of the resultant laminate (fired body), and the resultant laminate is fired at 850° C. for one hour. Thus, the sheet body 11 (before the reduction process) is formed. In this case, instead of using the YSZ tape, a ceramic sheet may be formed by a printing process on the lower surface of the sheet (that is to become the fuel electrode layer 11b) made of NiO and YSZ. Further, a ceria layer (CeO2) serving as a reaction preventing layer may be formed between the electrolyte layer and the air electrode layer. As a ceria, GDC (gadolinium doped ceria), SDC (samarium doped ceria) or the like may be used. Further, zircon having small thermal expansion coefficient may be added to the fuel electrode layer. By virtue of the addition of zircon, the mean thermal expansion coefficient of the fuel electrode layer is reduced, whereby the difference in the thermal expansion coefficient between the fuel electrode layer and the air electrode layer can be reduced. As a result, the warpage on the sheet body caused by the difference in thermal expansion coefficient between the layers in the sheet body can be reduced.
Manufacturing Separator
The separator 12 used for the assembly of the fuel cell 10 can be formed from a Ni-based heat-resistant alloy (e.g., ferritic SUS, INCONEL 600, HASTELLOY or the like) by a well-known technique such as etching or cutting.
Manufacturing Metal Mesh
The flat sheet-like SUS mesh 31 and the Ni mesh 31 used for the assembly of the fuel cell 10 can be formed from stainless steel (specifically, ferritic SUS) and Ni, respectively, by a well-known technique.
Ag-Plating and Vacuum Heat-Treatment on SUS Mesh
For the SUS mesh 31, in the air and at a high temperature, chromia (Cr2O3), which is an oxide having large electrical resistance, layer may be formed due to oxidation. Accordingly, when the SUS mesh 31 is subjected in the air and at a high temperature during the heat-treatment (will be described later) in the fabrication process of the stack structure, or during the operation of the fuel cell 10, chromia may be formed on the surface of the SUS mesh 31. Particularly, the formation of chromia layer on the surface of the upper end of the SUS mesh 31 (i.e., on the surface of the portion electrically connected to the air electrode layer 11c) leads to the increase in the electrical resistance of the fuel cell 10 as a whole and thereby the decrease in the output of the fuel cell 10 as a whole.
Therefore, it is preferred that, on the surface of the SUS mesh 31, an electrically conductive oxygen barrier layer for suppressing the oxidation of the surface while maintaining the electrical conductivity of the SUS mesh 31. In addition, for the Ni mesh 32, in the air and at a high temperature, an oxide may be formed due to oxidation. However, with a reduction process, the oxide is also reduced when NiO within the fuel electrode layer 11b is reduced. Accordingly, for the Ni mesh 32, it is not so necessary to daringly form an oxygen barrier layer on its surface. As described above, in the present embodiment, as shown in
As shown in
Therefore, in the present embodiment, as shown in
It has been revealed that after the SUS mesh 31 is further subjected to the vacuum heat-treatment in addition to the Ag-plating treatment as described above, it becomes difficult to form chromia on the surface of the SUS mesh 31 (i.e., at the boundary between the SUS mesh 31 and the Ag-plated layer), even though the SUS mesh 31 is placed at a high temperature, during the subsequent fabrication process of the fuel cell 10, or during the operation of the fuel cell 10 (will be described in detail). It is believed that this is because, in a negative pressure condition where the concentration of oxygen is low in the atmosphere (i.e., a condition wherein even if the Ag-plated layer detached, it is difficult to provide the surface of the SUS mesh 31 with oxygen), the boundary between the SUS mesh 31 and the Ag-plated layer is reacted and integrated by the heat-treatment, and thereby a strong oxygen barrier layer is formed on the surface of the SUS mesh 31.
Assembly of Stack Structure
After the necessary number of the sheet body 11 and the separator 12, the SUS mesh 31 and the Ni mesh 32 are prepared as described above, the assembly of the fuel cell 10 progresses as described below. The assembly of the fuel cell 10 will be described with reference to
Welding Metal Mesh to Separator
As shown in
Similarly, the upper end of the Ni mesh 32 is fixed to the lower surface of the plane portion 12a of the upper separator 122 by means of welding (or diffusion bonding). Thereby, the reliability of the electrical connection between the Ni mesh 32 and the upper separator 122 is secured.
Coating Adhesive Paste on Sheet Body
Then, as shown in
Similarly, for the sheet body 11 (refer to
Coating Sealant on Separator
Then, as shown in
Stacking Step
Then, as shown in
In addition, the upper end of the SUS mesh 31 (after the Ag-plating treatment and the vacuum heat-treatment) contacts the Ag paste film coated on the lower surface of the air electrode layer 11c. Thus, as shown in
Similarly, the lower end of the Ni mesh 32 contacts the Ni paste film coated on the upper surface of the fuel electrode layer 11b. Thus, the state, in which the fuel electrode layer 11b and the lower end of the Ni mesh 32 contact each other through the Ni paste, is obtained.
Heat-treatment
Next, the resultant stack structure is subject to a heat treatment (corresponding to the “second heat-treatment”), whereby the temperature of the stack structure is kept to be a predetermined temperature (e.g., 830° C.) for a predetermined time (e.g., 1 hr). As a result, the perimetric portion of the sheet body 11 and the perimetric portion of the separator 12 adjacent to the sheet body 11 are integrated and sealed (bonded). Consequently, the fuel channels 22 and the air channels 21 are airtightly formed and defined by the crystallized glass.
In addition, the Ag paste film is solidified to be an Ag fired film. Thus, the upper end of the SUS mesh 31 (after the Ag-plating treatment and the vacuum heat-treatment) is fixed with the lower surface of the air electrode layer 11c through the Ag fired film, and electrically connected with the air electrode layer 11c. Thus, by means of the Ag fired layer interposed between the SUS mesh 31 and the air electrode layer 11c, the reliability of the electrical connection between the SUS mesh 31 and the air electrode layer 11c is secured.
Similarly, the Ni paste film is solidified to be an Ni fired film. Thus, the lower end of the Ni mesh 32 is fixed with the upper surface of the fuel electrode layer 11b through the Ni fired film, and electrically connected with the fuel electrode layer 11b. Thus, by means of the Ni fired layer interposed between the Ni mesh 32 and the fuel electrode layer 11b, the reliability of the electrical connection between the Ni mesh 32 and the fuel electrode layer 11b is secured.
Reduction Process Step
Next, the stack structure is again subject to a heat treatment, so that the temperature of the stack structure is kept to be a predetermined temperature for a predetermined time. Simultaneously, a reduction gas (hydrogen gas in this embodiment) is introduced into the fuel channels 22. The reduction process is performed to the fuel electrode layers 11b due to the introduction of the reduction gas, whereby, of NiO and YSZ constituting the fuel electrode layer 11b, NiO is reduced. As a result, the fuel electrode layer 11b becomes a Ni—YSZ cermet, thereby being capable of serving as a fuel electrode (anode electrode). Thus, the assembly of the fuel cell 10 is completed.
Effect of Ag-Plating Treatment and Vacuum Heat-Treatment
As described above, in the present embodiment, the Ag-plating treatment and the vacuum heat-treatment are performed on the SUS mesh 31, and thereby a strong oxygen barrier layer is formed on the surface of the SUS mesh 31. Then, during the fabrication process of the fuel cell 10, in the state, in which the SUS mesh 31 is connected with the air electrode layer 11c through the Ag paste film, the above-described heat-treatment (corresponding to the “second heat-treatment”) is performed, wherein the SUS mesh is placed at a high temperature. Further, also when the fuel cell 10 operates after the completion of the assembly of the fuel cell 10, the SUS mesh is placed at a high temperature.
In the present embodiment, since the above-described strong oxygen barrier layer has been formed, even though the SUS mesh 31 is placed at a high temperature during the above-described fabrication process of the fuel cell 10, and during the operation of the fuel cell 10, no (or little) chromia is formed on the surface of the electrical connection portion with the Ag fired film (i.e., the air electrode layer 11c) (at the boundary between the SUS mesh 31 and the Ag-plated layer). Accordingly, the increase in the electrical resistance (internal resistance) of the fuel cell 10 as a whole due to the formation of chromia does not occur and, as a result, the decrease in the output of the fuel cell 10 as a whole due to the formation of chromia does not occur. In addition, the decrease in the output of the fuel cell 10 as a whole due to the “chromium poisoning” (described above) of the air electrode layer 11c can be suppressed as well.
The two experiments conducted in order to confirm this operation will be described below. In these two experiments, in order to compare the structures of electrical connection between the SUS mesh 31 and the air electrode layer 11c with that of the present embodiment, the following three comparative examples (Comparative Examples 1 to 3) shown in
Specifically, in Comparative Example 1 (refer to
In Comparative Example 2 (refer to
In Comparative Example 3 (refer to
First Experiment
In the first experiment, the apparatus, whose schematic configuration is shown in
Accurately, the resistance value R1 is a sum of an internal resistance (bulk resistance) of the adhesive fired body and the resistances (interfacial resistances) at the respective “boundaries with the adhesive fired body” on the two SUS bars. However, the bulk resistance is sufficiently smaller than the interfacial resistances. Therefore, it can be assumed that the resistance value R1 may be determined mainly based on the interfacial resistances. In the first experiment, to the apparatus, the above-described present embodiment and Comparative Examples 1 to 3 are applied, and the respective resistance values, R1s, are evaluated. The resistance value R1 increases due to the formation of chromia on the surface of the electrical connection portion with the adhesive fired body on the SUS bars.
Specifically, in the first experiment, SUS bars in a size of 5 mm×5 mm×20 mm and with its surface finished with sand-paper with a roughness of #800 were used. The thickness of the plated layer was adjusted by controlling the film-forming condition. The thickness of the adhesive fired body (=the distance between the respective “boundaries with the adhesive fired body” on the two SUS bars) was adjusted to be constantly 50 μm by controlling the pressure during the heat-treatment for firing the adhesive paste.
In the case of the present embodiment, an Ag-plated layer with a thickness of 10 μm was formed on the whole surface of the two SUS bars (as a base layer, an extremely thin Ni-plated layer being formed). On the two SUS bars after the plating treatment, the vacuum heat-treatment was performed. As the vacuum heat-treatment, under a vacuum atmosphere of 1×10−3 Pa, at 800° C., for 1 hr, a heat-treatment was performed. The two SUS bars after the plating treatment and the vacuum heat-treatment were bonded through the Ag paste. On the bonded body, the above-described heat-treatment (800° C., 1 hr) is performed to fire the Ag paste. In this state, the resistance value R1 is measured.
In the case of Comparative Example 1, the two SUS bars, on which neither the plating treatment nor the vacuum heat-treatment had been performed, were bonded through the Ag paste. On the bonded body, the above-described heat-treatment (850° C., 1 hr) is performed to fire the Ag paste. In this state, the resistance value R1 is measured.
In the case of Comparative Example 2, an Ag-plated layer was formed on the whole surface of the two SUS bars (on which an extremely thin Ni-plated layer had been formed as a base layer). The two SUS bars, on which the plating treatment had been performed, but the vacuum heat-treatment had not been performed, were bonded through the Ag paste. On the bonded body, the above-described heat-treatment (850° C., 1 hr) is performed to fire the Ag paste. In this state, the resistance value R1 is measured.
In the case of Comparative Example 3, the two SUS bars, on which neither the plating treatment nor the vacuum heat-treatment had been performed, were bonded through the Pt paste. On the bonded body, the above-described heat-treatment (850° C., 1 hr) is performed to fire the Pt paste. In this state, the resistance value R1 is measured.
The resistance values, R1s, (specifically, the resistant values, Rtotals) were measured by using a well-known direct current four terminal method. The atmospheric temperature on the measurement was 750° C. The resistance values, R1s, were measured from the beginning of the measurement to 1000 hrs. The results of the resistance values, R1, measured in this first experiment are shown in
As shown in
The significance for measuring the resistance value R1 from the beginning of the measurement to 1000 hrs will be described below. Recently, as applications of a solid oxide fuel cell (SOFC), mobile power supplies, dispersed power sources, stationary power supplies and the like have been intended. In these fields, a long-term durability around thousands hrs to dozens thousand hrs is required. Specifically, for example, in the case of stationary power supplies, “the degradation rate of 10% or less in a resistance value after 40000 hrs” may be required as a development objective, and, in this case, the development objective becomes “the degradation rate of 0.25% or less in a resistance value” when converted into that after 1000 hrs. Thus, a steadiness in resistance value for at least about 1000 hrs is essential. Accordingly, from such a point of view, it can be concluded that the present embodiment with a very high steadiness of a resistance value is superior to Comparative Example 3 with a resistance value increasing with time.
In addition, as shown in
Second Experiment
In the second experiment, the stack structures were actually manufactured. In the experiment, a sheet body of a fuel-electrode-support-type (the fuel electrode layer serves as a support substrate) was used to constituting the stack structures. This sheet body is square having one side of 3 cm as viewed in plane, and includes an electrolyte layer (thickness: 3 μm) made of 8YSZ, a fuel electrode layer (thickness: 150 μm) made of NiO-8YSZ, and an air electrode layer (thickness: 15 μm) made of LSCF, those layers being stacked. As described above, a ceria (GDC and the like) layer may be interposed, as a reaction preventing layer, between the electrolyte layer and the air electrode layer. Three-layer stacks were manufactured in the stacking step by using this sheet body. In the second experiment, the output density in operation of the three-layer stacks is evaluated. Small output density of the stack results from the formation of chromia on the surface of the electrical connection portion with the metal fired film (accordingly, the air electrode layer) on the SUS mesh.
Such stack structures were respectively manufactured for the present embodiment, and Comparative Examples 1 to 3 having the structures shown in
As shown in
The results in
More specifically, as shown in
In case of the Comparative Example 1 (refer to
In case of the Comparative Example 2 (refer to
In case of the Comparative Example 3 (refer to
When chromia is formed on the surface of the electrical connection portion with the metal fired film (accordingly, the air electrode layer 11c) on the SUS mesh 31, the electrical resistance of the stack structure increases. However, even when chromia is formed on the surface excluding the surface of the electrical connection portion with the metal fired film (accordingly, the air electrode layer 11c) on the SUS mesh 31, the electrical resistance of the stack structure does not increase. Accordingly, in the case of Comparative Example 3, the output density comparable to that in the present embodiment can be obtained.
The results of the first and second experiments will be analyzed below. As shown in
As shown in
To the contrary, as shown in
Further, as shown in
In addition, for a polymer electrolyte fuel cell (PEFC), which is antecedent to a solid oxide fuel cell (SOFC) in the development of fuel cells, very expensive Pt is essential. Accordingly, in order to obtain the superiority over PEFC on the commercialization of SOFC, nonuse of Pt is essential. From such point of view as well, it can be expected that the highly reliable present embodiment wherein Pt is not used and, as described above, high output can be steadily obtained regardless of the structures of a cell and stack, will facilitate the commercialization of SOFC.
Most Suitable Condition for Vacuum Heat-Treatment
Next, the most suitable condition for the vacuum heat-treatment performed after the Ag-plating treatment on the SUS mesh 31 will be described. In accordance with the investigation by the inventors, it was revealed that, in the vacuum heat-treatment, the degree of vacuum (pressure) is preferably from 10−5 to 10−1 Pa, the temperature is preferably from 500 to 900° C., and the duration time is preferably from 10 minutes to 3 hrs. A test conducted in order to confirm this will be described below.
In this test, as a test piece, the same SUS bars as those used in the above-described first experiment were used. For each of plural numbers of the test pieces, on which Ag-plated layer had been formed, the vacuum heat-treatment was performed under a different condition. For these plural numbers of test piece, based on the initial resistance values and the observation of the surfaces and the cross-sections thereof (for the existence or nonexistence of chromia) by means of scanning electron microscopy (SEM), the conditions for the vacuum heat-treatment were evaluated. Regarding the Ag-plated layer, from the result of the prior discussion, i.e., “with a thickness of 1 μm or less, the effect as an oxygen barrier layer is low, and with a thickness of 20 μm or more, the possibility of the detachment of the Ag-plated layer is high”, it has been revealed that the thickness of the Ag-plated layer is preferably from 1 to 20 μm. Accordingly, in this test, for plural numbers of the test pieces, the thickness of the Ag-plated layer was constant at 10 μm. The results of this test are shown in the table below.
Degree of
Duration
Condi-
Vacuum
Temp.
Time
tion
[Pa]
[° C.]
[min]
Result
Evaluation
1
1
800
60
Bad
No Barrier Effect
(Large Resistance)
2
10−1
800
60
Good
Acceptable
3
2 × 10−2
800
60
Good
Acceptable
4
1 × 10−3
800
60
Good
Acceptable
5
3 × 10−4
800
60
Good
Acceptable
6
1 × 10−5
800
60
Good
Acceptable
7
1 × 10−3
450
60
Bad
No Barrier Effect
(Large Resistance)
8
1 × 10−3
500
60
Good
Acceptable
9
1 × 10−3
600
60
Good
Acceptable
10
1 × 10−3
700
60
Good
Acceptable
11
1 × 10−3
800
60
Good
Acceptable
12
1 × 10−3
900
60
Good
Acceptable
13
1 × 10−3
950
60
Bad
Failure Due to
Deterioration of
Ag-plated Layer
14
1 × 10−3
800
5
Bad
No Barrier Effect
(Large Resistance)
15
1 × 10−3
800
10
Good
Acceptable
16
1 × 10−3
800
30
Good
Acceptable
17
1 × 10−3
800
120
Good
Acceptable
18
1 × 10−3
800
180
Good
Acceptable
As can be understood from the above table, at a degree of vacuum (pressure) of higher than 1×10−1 Pa, there is no effect of oxygen barrier layer, and the initial resistance is very large (refer to Condition 1). On the other hand, at a degree of vacuum in the range of 1×10−5 to 1×10−1 Pa, the initial resistance is small, and no formation of chromia can be observed by means of SEM (refer to Conditions 2 to 6). At a temperature of lower than 500° C., there is no effect of oxygen barrier layer, and the initial resistance is very large (refer to Condition 7). At a temperature of higher than 900° C., the deterioration of the Ag-plated layer was observed by means of SEM (refer to Condition 13). On the other hand, at a temperature in the range of 500 to 900° C., the initial resistance is small, and no formation of chromia can be observed by means of SEM (refer to Conditions 8 to 12). With duration time of shorter than 10 minutes, there is no effect of oxygen barrier layer, and the initial resistance is very large (refer to Condition 14). On the other hand, with duration time in the range of 10 minutes to 3 hrs, the initial resistance is small, and no formation of chromia can be observed by means of SEM (refer to Conditions 15 to 18). From the above, in the vacuum heat-treatment, the degree of vacuum is preferably from 10−5 to 10−1 Pa, the temperature is preferably from 500 to 900° C., and the duration time is preferably from 10 minutes to 3 hrs.
Thickness of Chromia Layer
The measurement results of the thickness of the “layer containing chromia (Cr2O3)” (hereinafter, referred to as “chromia layer”) formed at the boundary between the SUS mesh 31 and the Ag-plated layer (or Ag fired film) will be described below.
As apparent from
Plural numbers (N=5) of samples corresponding to Comparative Example 1 were manufactured, and the thickness of a chromia layer was calculated for each of the samples. The thickness of a chromia layer was defined as a “film thickness of the dark gray portion formed around the boundary in the reflection electron image by means of FE-SEM” immediately after the completion of the assembly of SOFC, or under a condition where the total operation period of SOFC is 100 hours or less. According to this definition, the thickness of a chromia layer was from 1.0 to 1.2 μm. The proportion (Dcr2/Dcr1) of the Cr concentration (peak value) in the chromia layer, Dcr2, (refer to
To the contrary,
As apparent from
Plural numbers (N=5) of samples corresponding to the present embodiment were manufactured, and the thickness of a chromia layer was calculated for each of the samples. The definition of “thickness of a chromia layer” was the same as described above. Among these plural numbers of samples, the condition for the vacuum heat-treatment, i.e., the combination of degree of vacuum (range: 10−5 to 10−1 Pa), temperature (range: 500 to 900° C.), and duration time (range: 10 minutes to 3 hrs) was varied respectively. As a result, the thickness of a chromia layer was extremely small, (from under the measuring limit of SEM to) less than 0.8 μm. The lower limit of the thickness of a chromia layer was less than the measuring limit of SEM. The measuring limit of SEM was 0.01 μm. The proportion (Dcr2/Dcr1) of the Cr concentration (peak value) in the chromia layer, Dcr2, (refer to
As can be understood from the above results, in the present embodiment, as compared with Comparative Example 1, the thickness of the chromia layer formed at the boundary between the SUS mesh 31 (the “conductive member”) and the Ag-plated layer (or Ag fired film) (the “metal film”) is extremely thin. It is believed that this greatly contributes to the fact that the electrical resistance (internal resistance) of the electrical connection portion between the SUS mesh 31 and the air electrode layer 11c in the present embodiment is sufficiently small as compared with that in Comparative Example 1.
As described above, the solid oxide fuel cell according to the embodiment of the present invention has the stack structure formed by stacking the sheet bodies 11, each of which comprises three layers of the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c, and the separators 12 in alternating layers. In the air channel 21 defined between the air electrode 11c and the separator 12 facing the air electrode layer 11c, the SUS mesh 31 made of stainless steel for electrically connecting both of them is confined. On the surface of the SUS mesh 31, previously by itself before the assembly of the stack structure, the Ag-plating treatment is performed and further the vacuum heat-treatment is performed. Thereby, at a high temperature during the assembly process of the stack structure, and during the operation of the fuel cell, on the surface of the electrical connection portion with the air electrode layer 11c on the SUS mesh 31, chromia (Cr2O3), which is the oxide of stainless steel and has a high electrical resistance, is not formed. Accordingly, the increase in the electrical resistance (internal resistance) of the fuel cell as a whole due to the formation of chromia can be suppressed, and consequently the decrease in the output of the fuel cell as a whole can be suppressed.
The present invention is not limited to the above-described embodiment, but can be modified in various other forms without departing from the scope of the present invention. For example, although the SUS mesh 31 and the air electrode layer 11c are electrically connected through the Ag fired film in the above-described embodiment, the SUS mesh 31 and the air electrode layer 11c may directly contact to be electrically connected without the interposition of the Ag fired film.
Although Ag paste is adopted as an adhesive paste interposing between the SUS mesh 31 and the air electrode layer 11c in the above-described embodiment, electrically conductive ceramic paste may be used. Although an Ag-plating treatment is adopted as a metalizing plating treatment performed on the surface of the SUS mesh 31 in the above-described embodiment, a Zn-plating treatment may be adopted.
Although a metal mesh (SUS mesh) is adopted as a “conductive member” for electrically connecting the air electrode layer 11c and the lower separator 121 in the above-described embodiment, it may be one or plural rod-like electrically conductive bodies connecting the air electrode layer 11c and the lower separator 121.
In the above-described embodiment, the fuel electrode layer 11b can be formed from, for example, platinum, platinum-zirconia cermet, platinum-cerium oxide cermet, ruthenium, ruthenium-zirconia cermet or the like.
Also, the air electrode layer 11c can be formed from, for example, lanthanum-containing perovskite-type complex oxide (e.g., lanthanum cobaltite, in addition to the above-mentioned lanthanum manganite). Lanthanum cobaltite and lanthanum manganite may be doped with strontium, calcium, chromium, cobalt (in the case of the lanthanum manganite), iron, nickel, aluminum, or the like. Also, the air electrode layer 11c may be formed from palladium, platinum, ruthenium, platinum-zirconia cermet, palladium-zirconia cermet, ruthenium-zirconia cermet, platinum-cerium oxide cermet, palladium-cerium oxide cermet, or ruthenium-cerium oxide cermet.
In the above-mentioned embodiment, the sheet body 11 and the separator 12 have a planar shape of square. However, the sheet body 11 and the separator 12 may have a planar shape of rectangle, circle, ellipse, etc.
In addition, in the above-described embodiment, the sheet body 11 comprising a solid electrolyte layer 11a and a fuel electrode layer 11b and an air electrode layer 11c is used as a “reaction member”, and the stack structure, wherein a metal mesh (SUS mesh 31) is used as an “electrically conductive member”, is adopted (refer to
In the stack structure shown in
Nanataki, Tsutomu, Nakamura, Toshiyuki, Ohmori, Makoto, Shinkai, Masayuki
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